Bevelling of cylinders



Sept. 17, 1957 H. l. OSHRY ET AL 2,806,334'

BEVELLING OF CYLI'NDERS Filed Oct. 10, 1955 United States Patent BEVELLING OF CYLINDERS Howard I. Oshry and Richard C. Esser, Erie, Pa., asslgnors to Erie Resistor Corporation, Erie, Pa., a corporation of Pennsylvania Application October 10, 1955, Serial No. 539,371 2 Claims. (Cl. 51-281) trifugal force against the inner surface of the container in a thin layer which rotates at essentially surface speed. The thin layer of liquid (much less than the diameter of the tubes) exerts insuflicient force to drag the tubes around at the surface velocity of the container. The tubes collect by gravity in a single thickness layer occupying a.

large part of the lowermost half of the inner surface of the container. The tubes in the layer are distributed in a random fashion with many of the tubes in groups having axes parallel to each other but with a random distribution so the axes of individual tubes vary all the way from parallel to the axis of the container to at right angles to the axis of the container. Adjacent tubes are in contact with each other so the friction between adjacent tubes restricts rotation of the tubes on their axes. There is a continual redistribution of the positions of individual tubes both in inclination of the axes of the tubes and in rotation of the tubes on their axes. This is sufiicient so that all parts of the ends of the tubes come into contact with the liquid on the inner surface of the container. The redistribution is at such a slow rate compared to the surface velocity of the container that the grinding action is as though the individual tubes were held relatively stationary by gravity against the wet film of abrasive suspension. No matter which way the tubes are inclined, only the end edges contact the container and only the end edges are bevelled. This is advantageous in the manufacture of tubular capacitors.

In the drawing, Fig. 1 is a longitudinal section through a tubular condenser; Fig. 2 is a section on line 22 of Fig. 1; Fig. 3 is a longitudinal section through a metal coated tubular ceramic used in the manufacture of the Fig. l and 2 condenser; Fig. 4 is a section through a spherical container used to bevel the ends of the tubes, the section being through the axis of rotation of the container; Fig. 5 is an end view of the spherical container and Fig. 6 is a fragmentary view illustrating the grinding action by which the ends of the tubes are bevelled.

The invention is shown applied to the manufacture of tubular capacitors having a tubular ceramic dielectric 1 provided with inner and outer electrodes 2 and 3. An insulating band is provided at each end of the outer electrode 3 by the bevelled portions 4. The capacitor will ordinarily have a length of approximately and a diameter of to 4". The wall thickness will, of course, vary with the requirements for mechanical strength and capacity.

In the manufacture of the condenser a ceramic tube 5 with square ends 6 is coated over the entire inner, outer and end surfaces with a suitable metal coating 7. At this stage, the ceramic dielectric 5 is completely enclosed by the metal coating 7 and cannot be used as a capacitor. In order to be usable as a capacitor, an insulating band 2,806,334 Patented Sept. 17, 1957 ice must be provided between the metal coatings on the inner and outer surfaces of the tubular dielectric which can be done by bevelling the ends as shown at 4 in Fig. 1.

In order to bevel the ends of the metal coated tubes illustrated in Fig. 3 and thereby obtain usable capacitors, a large batch is loaded into a spherical container 8 illustrated in Figs. 4 and 5 along with a small quantity of water and grinding compound. For the /8" length tubes, 8. suitable size container would be a sphere 12" in diameter into which would be loaded from 800 to 1,000 of the metal coated ceramic tubes illustrated in Fig. 3 along with from 20 to 30 cc. of water and /2 teaspoonful of grinding compound. The spherical container would then be rotated at a speed of substantially 500 R. P. M. and within 10 to 15 minutes all of the ceramic tubes will be bevelled as indicated at 4 in Fig. 1 without any appreciable abrasion of the outer metal coating which is to form the outer electrode 3 of the finished condenser.

The bevelling action is definitely not tumbling. At the speed of rotation of 500 R. P. M., the surface speed at thediameter of the spherical container would result in a centrifugal force more than 40 times that of gravity. Accordingly, the extremely high speed of rotation of the spherical container eliminates any tumbling action which must take place at speeds of rotation where centrigufal force is less than that of gravity. The liquid, together with the grinding compound, collects in a thin layer 9 (2 to 4 mils thick) on the inner surface of the container. As shown in Fig. 6, the thickness of this layer is small compared to any dimension of the ceramic tubes. The

small thickness of the layer 9 exerts insufficient drag on the ceramic tubes to cause them to rotate at the surface speed of the container. The extreme thinness of the layer 9 is important. As soon as the depth of the liquid is increased so that the tubes are immersed, the action is entirely different.

With this small amount of liquid and high speed of rotation of the spherical container, the tubes collect in a layer in the lower part of the container having outer boundaries generally indicated by the dotted lines 10 and 11 in Figs. 4 and 5. Fig. 4, which is a sectional View, shOWs how the tubes are dragged up along the inside of the container to an elevation short of the axis of the container. Thissame effect is illustrated in Fig. 5 which is an end view. The distribution of the metal coated ceramic tubes 5 is random. As illustrated in both Figs. 4 and 5, there are many groups of tubes with axes parallel to each other but there are also single tubes and adjacent groups need not necessarily have their axes parallel to each other. The alignment is entirely random. The tubes collect in a single layer thickness. From time to time individual tubes at the boundaries of the layer may break away from the upstream edge and fly across the container and rejoin the layer at the downstream edge. This is not a regular occurrence although it may take place if the speed of rotation is too high or if the depth of liquid is too great. This action is usually avoided because of the possibility of cracking the tubes as they strike after flying across the container. To cut down this action, the speed of rotation is slightly reduced.

Because of the random distribution of the tubes it is difiicult to describe the action. As individual tubes are watched, their axes continually shift from parallel to crosswise to the axis rotation of the container. There is also a very slow but intermittent rotation of the individual tubes on their axes. Apparently the individual tubes bounce and move out of contact with each other and with the abrasive liquid layer 9. As the tubes return, their position is slightly changed. Because of this continual change in position or redistribution of the positions of the individual tubes, a very sharply defined and uniform bevel is produced at each end of the tube. This indicates that there is essentially uniform grinding away of the ends of the tubes at a bevel corresponding to the curvature of the inner surface of the spherical container. It will be noted that no matter how the axes of the individual tubes are inclined, the tubes lie chordwise across the inner surface of the container in position to produce the bevelling action desired. The bevelling is apparently wet grinding due to slippage between the tubes and the layer 9 of the liquid suspension of grinding particles. The tubes which are held by gravity against this liquid suspension in the lower part of the spherical container and remain essentially within the area so defined by the dotted lines 10 and 11. The motion of the individual tubes is confined to relatively slow changes in the inclination of the axes of the tubes and in rotation of the individual tubes on their axes. Accordingly, the only forces acting on the tubes are gravity and the friction between the tubes and the abrasive liquid layer 9. The abrasive layer 9, because of its thickness, must rotate at substantially the surface speed of the container. The grinding action is accordingly that which would be obtained if a high speed jet of liquid with abrasive articles suspended therein were directed against the corners of a relatively stationary tube.

The described grinding action will not take place if there is only a single tube 5 within the container. A single tube rotates at essentially the surface speed of the container and is held outward against the inner walls thereof by centrifugal force. The action with a single tube is accordingly entirely different from the action of a large number of tubes. A .single tube has nothing to restrain rotation on its axis. Two adjacent tubes in contact with each other exert a friction force which restricts the rotation of the individual tubes on their axes. Furthermore, with a single tube, both the tube and the liquid abrasivesuspension is held at the region of greatest diameter of the sphere. With a large batch of tubes, the tubes are not all at the region of maximum diameter but spread out to regions of lesser diameter. There is accordingly a difference in the rate of slippage between the tubes and liquid which may further help in the redistribution of the individual tubes with the container Although the invention has been shown as applied to the manufacture of tubular condensers, the same bevelling action would take place with any cylinders. From one aspect of the invention, the tubes can be considered as cylinders with a center bore.

This application is an improvement on commonly owned application Serial No. 475,703 filed December 16, 1954 which should be considered as prior art for this application.

What is claimed as new is:

1. The method of bevelling the end edges of cylinders which comprises loading a batch of cylinders into a spherical container along with a liquid abrasive suspension, said container having a radius of curvature such that the cylinders lying chordwise on the inner surface of the container in any orientation intersect the surface of the container at the desired angle of bevel, said liquid suspension being of quantity only sufiicient to form a film on the inner surface of the container of thickness equal to a small fraction of the diameter of the cylinders, and rotating the container at a speed such that centrifugal force at the surface is many times gravity and the cylinders predominantly lie quietly in a single thickness layer in the lower part of the container With adjacent cylinders substantially in contact with each other but with no regular or maintained pattern of alignment with each other or with the axis of rotation of the container.

2. The method of bevelling the end edges of dielectric tubes coated with metal over inner, outer and end surfaces so as to provide an insulatingband between the coatings on the inner and outer surfaces which comprises loading a batch of tubes into a spherical container along With a liquid abrasive suspension, said container having a radius of curvature such that the tubes lying chordwise on the inner surface of the container in any orientation intersect the surface of the container at the desired angle of bevel, and rotating the container at a speed such that centrifugal force at the surface is many times gravity and the tubes predominantly lie quietly in a single thickness layer in the lower part of the container with adjacent tubes substantially in contact with each other but with no regular or maintained pattern of alignment with each other or with the axis of rotation of the container.

' I References Cited in the file of this patent UNITED STATES PATENTS 1,360,511 Emerson Nov. 30, 1920 2,387,136 Fruth Oct. 16, 1945 2,387,141 Fruth Oct. 16, 1945 2,664,675 Monica Jan. 5, 1954 

